Starting device for alternating-current induction-motors.



PATENTED AUG. 30, 19% H. s. MEYER.

STARTING DEVICE FOR ALTBRNATING CURRENT INDUCTION MOTORS.

APPLICATION FILED NOV. 7, 1902. no MODEL.

F F l B P r mtg.

UNITED STATES HANS S. MEYER, OF RUGBY, ENGLAND, ASSIGN OR TO GENERAL ELECTRIC Patented August 30, 1904.

PATENT OFrIcE.

COMPANY, A CORPORATION OF NEW YORK.

STARTING DEVICE FOR ALTERNATlNG-CURRENT INDUCTION-MOTORS.

EPECIFICATION forming part of Letters Patent No. 769,098, dated August 30, 1904.

Application filed November 7, 1902. Serial No. 130,481- (No model.)

To all whom, it may concern:

Be it known that I, HANS S. MEYER, a subject of the Emperor of Germany, residing at Rugby, England, have invented certain new and useful Improvements in Starting Devices for Alternating-Current Induction-lVlotors, of which the following is a specification.

In order to secure close regulation and high efliciency, the armature-windings of induction-motors are ordinarily designed so as to have a low resistance; but when thus designed the starting torque is comparatively small and the current taken from the line at starting is large and considerably out of phase with the impressed electromotive force.

' Various expedients have been resorted to for the purpose of securing a large starting torque combined with high efficiency under normal loads. For example, the most common arrangement is to provide a separate resistance which is arranged to be connected into the motor-circuit at starting and gradually cut out as the motor comes up to speed. This arrangement, however, involves 0bjectionable losses, and the space occupied by the resistance-boxes is considerable. Moreover, since the additional resistance is in most cases entirely non-inductivea very large resistance is required for cutting the current down to, say, its full load-running value, as is necessary in many cases. It has also been proposed to provide the rotor with a second winding of high resistance, which is used only during the period of starting, or to mount the resistance inside of the rotor-spider, so that it revolves therewith, the resistance in the latter case being gradually cut out of the rotor-circuit as the motor comes up to speed. The usefulness of the resistance, however, in either of these arrangements is limited to the period of starting, which of course in most motors forms a very small percentage of the total working period. Besides, it takes up space which could be more efliciently filled by material which might be active all the time and help to increase the efiiciency of the service.

My present invention has for its object to attain a more efficient use of the resistance during both the starting and running periods and to reduce it in size to the smallest possible amount. To this end I provide in addition to the ordinary low-resistance phase winding and in circuit therewith a winding of comparatively high resistance, which, according to one portion of my invention, is constructed of iron or other magnetic material, so that it will serve to conduct part of the useful magnetic flux of the secondary member during the running of the motor, acting in this respect in the same manner as the iron in which it is embedded. The two windings constitute a single winding having a low-resistance and a high-resistance portion. The high-resistance winding is arranged to be cut out of circuit during starting in the same manner as the ordinary resistance in the secondary circuit would be cut out.

, In carrying my invention into effect according to one modification I construct the slots of the secondary member of sufficient depth to provide room below the ordinary phase winding for the auxiliary starting-resistance winding. This latter consists of iron wires insulated in a suitable manner from each other and from the main winding. The resistancewinding is connected in series with the main winding, and its resistance is graduated in suitable steps, the extremities of each step in each phase being connected to the contacts of a suitable short-circuiting switch which may be worked either by hand or automatically and which is arranged to revolve with the rotor, thus avoiding the use of slip-rings.

My invention will be better understood by reference to the following description, taken in connection with the accompanying drawings, in which- Figure 1 illustrates diagrammatically the secondary winding of an induction-motor constructed in accordance with my invention. Fig. 2 is a diagrammatic representation of a switch by means of which the high-resistance sections of the winding of Fig. 1 may be gradually cut out of circuit; and Fig. 3 is a view in cross-section of one of the slots of the secondary member, showing the dimensions and relative arrangement in the slot of the several sections of the winding according to one embodiment of my invention.

Referring to the drawings, E E E represent the several sections of an ordinary lowresistance phase winding for the secondary member of an induction-motor. eral sections taken together constitute a single winding, which I have indicated by E in the drawings.

The several sections of the resistance-winding are indicated by the letters F, G, and H, respectively. In starting, the connections for the winding E are through the several sections of the winding F, G, and H,the terminals of the latter winding, (0 a (0 being electrically connected together. The first movement of the short-circuiting switch operates to electrically connect the points 5, b and I), and therefore to short-circuit the portion H of the resistancewinding. The next movement of the switch operates to electrically connect the points 0, c and 0 and therefore to cut out of circuit the resistancesection G, and the final movement of the short-circuiting switch electrically connects the points (Z, (Z and (Z thus short-circuiting the winding E on itself without resistance in circuit therewith. The arrangement ofthe winding in the slots of the secondary member is indicated in Fig. 3, in which the four square conductors occupying the upper portion of the slot constitute a part of winding E of Fig. 1 and the iron wires located in the bottom of the slot portions of the winding F, G, and H of Fig. 1.

. The short-circuiting switch, by means of which the various sections of the resistancewinding are cut out of circuit, may be of any desired construction, and in Fig. 2 I have illustrated diagrammatically one of the constructions that may be employed. Referring to this figure, it will be noted that the points d (Z (Z are connected to contacts D, the points 0 0 0 to contacts C, and the points 6' I) b to contacts B. Other contacts, F, are provided, on which the movable contacts J of the shortcircuiting switch normally rest. The points a (L2 a are permanently electrically connected by grounding them on the framework of the secondary member, as indicated in Fig. 2. The contacts J of the short-circuiting switch are moved forward over the contacts B, C, and D in order to cut the resistance-winding out of circuit in the manner already described in connection with Fig. 1. The arrangement of the contacts B, G, and D. as shown in the drawings, is such that the corresponding sections of the different phases of the resistance winding are cut out simultaneously; but evidently by slightly displacing the contacts marked by the same letter with reference to one another the passage of the switch-contacts J might be made to cut out the corresponding sections of the resistance-winding These sevsuccessively, so as to give a greater number of resistance-steps. The contacts J may be moved by hand, a suitable construction for accomplishing this result being shown in patent to H. G. Reist, No. 678,034, dated July 9, 1901, or they may be arranged to be moved by an automatic device responsive to changes in the speed. i

The slots of the secondary member should be arranged in such a manner that, the iron wire will fill the bottom part of the slot in the best possible manner to afford an easy path for the magnetic lines of force. The number of resistance-steps and the size of the conductors composing the different sections of the resistance-winding will of course be arranged according to the capacity and the individual design of any particular motor. In order that the resistance-winding may be most effectively arranged, the cross-section of the conductors constituting the same should increase gradually from the first step when the entire resistance-winding is in circuit with the low-resistance phase winding, so as to give a resistance diminishing according to a geometrical progression, or in any other way that may be desirable. In the particular arrangement which I have illustrated in Fig. 3 the six iron wires constituting the resistance portion of the winding are intended to be connected all in series, so as to give for the first section to be cut out the three small wires having a large resistance, for the second section the two larger wires having a smaller resistance and a larger cross-section, and for the third section the largest wire having the smallest resistance and largest cross-section.

The inductionmotor being essentially a transformer it will be understood that with the above arrangement of the resistance-winding it is possible to keep approximately the same maximum current density on each step, for since all of the resistance-Wires are in series the current in the secondary winding at each step will be increasing relatively to the current in the primary inducing-winding in proportion to the diminution taking place in the turns of the secondary circuit inductively acted upon by the primary flux, thereby re quiring a larger cross-section of conductor at each step for the same current density. On the other hand, it is possible by this arrangement to greatly reduce the amount of resistance material required, since at the steps where large resistance is desired the current will be reduced in proportion to the number of turns added as resistance, and therefore a smaller cross-section of wire can be utilized, which means that its resistance increases as the square of the reduction in cross-section.

By increasing the depth of the slot in comparison to its width the current taken during the period of starting may also be reduced. owing to the increased self-induction which these slots introduce. This will reduce still further the resistance required for limiting the current at the starting, while the starting torque will not be. materially diminished, as is the case in devices depending on the increased self-induction only.

While the motor is running, only the upper portion of the slot occupied by the main winding is effective, the remainder of the slot being occupied by wire which is cut out of circuit and only magnetically active, giving the equivalent of a shallow slot and low self-induction, which means an increased power factor during the normal operation of the motor.

The iron wire'being part of the secondary circuit during starting will also have an actual resistance which in proportion to the induced frequency is much higher than the ordinary ohmic resistance of the circuit. This is due to what is commonly called the skin effect, which is at a maximum at starting, when the frequency of the current in the secondary winding is the same as the frequency of the current in the primary and decreases as the motor runs up to speed, reaching a minimum when the speed of the secondary member approaches synchronism. Thus in addition to the change in resistance provided by the shortcircuiting switch and the resistance-steps a reduction in resistance in proportion to the frequency is obtained. A further advantage is also obtained by using the useful magnetic material for obtaining impedance at starting instead of having a special iron core for obtaining such impedance.

It will thus be seen that according to my invention an induction motor can be constructed which will have a high efiiciency during running and a high torque at starting, with a resistance which is greatly reduced in size below that ordinarily employed, by so placing it that its actual and apparent value is increased, so that a considerable saving in space is effected. Moreover, this resistance is useful during the whole working period of the motor, thereby reducing the active material required for the motor and securing at the same time a more gradual starting, due to the combined action of the resistance-steps, the varying impedance of the resistance-winding, and the so-called skin eflect of the conductor constituting the said winding.

What I claim as new, and desire to secure by Letters Patent of the United States, is-

1. In an alternating-current induction-motor, a secondary member provided with an ordinary low-resistance winding adapted toordinary low-resistance winding and a highwindings and finally to short-circuit the lowresistance winding on itself.

3. A winding for the secondary member of an alternating-current induction-motor, comprising a low-resistance portion and a highresistance portion connected in series and.

means for short-circuiting the low-resistance portion on itself.

A. In an alternating-current induction-motor, a winding for the secondary member comprising an ordinary low-resistancewinding and a. high-resistance winding having its turns distributed over the same secondary member and connected in a closed circuit in series with said low-resistance winding and means for short-circuiting the said low-resistance winding on itself.

5. A winding for the secondary member of an alternating-current induction-motor, comprising a low-resistance portion adapted to be SllOl'lJ-rCllClllbBd on itself when the motor is running, and another portion adapted to serve as a resistance in circuit with the low-resistance portion at starting.

6. The combination with the ordinary lowresistarice secondary winding of an inductionmotor, of a second winding wound in the same slots therewith and adapted to serve as a resistance in circuit with the said low-resistance winding at starting, and means for cut ting said second winding out of circuit as the motor comes up to speed.

7 The combination with the slotted secondary member of an induction-motor, of a lowresistance winding. a resistance-winding of magnetic material connected in circuit therewith, and means for cutting said resistancewinding out of circuit.

8. The combination with the ordinary lowresistance winding of an induction-motor, of a second winding of magnetic material wound in the same slots and connected in circuit therewith, and means for cutting said second winding out of circuit.

9. An alternating-current induction-motor having its secondary member provided with a winding composed in part of low-resistance material and in part of magnetic material of high resistance, both portions of the said winding being wound in the same slots, and means for cutting the high-resistance portion of said winding out of circuit.

10. A winding for the secondary member of an induction-motor, comprising a low-resistance portion, and in circuit therewith a portion of comparatively high resistance, and means for cutting the high-resistance portion out of circuit.

11. A Winding for the secondary member of an induction-motor, comprising a low-resistance portion and in circuit therewith a portion'of comparatively high resistance constructed of magnetic material, both portions of thesaid Winding being Wound in the same slots with the portion constructed of magnetic material at the bottom of the slot.

12. A winding for the secondary member of an induction-motor, comprising a low-resistance portion and in circuit therewith a portion of comparatively high resistance constructed of magnetic material, the portion constructed of magnetic material being wou nd in sections of gradually-increasing cross-section to accommodate the increasing current flowing in the low-resistance portion as the successive sections are cut out of circuit.

13. A winding for the secondary member of an induction-motor comprising a low-resistance portion and in circuit therewith a portion of comparatively high resistance, the high-resistance portion being wound in sections of gradually-increasing cross-section to accommodate the increasing current flowing in the secondary winding as the successive sections are cut out of circuit.

In Witness whereof I have hereunto set my hand this 29th day of October, 1902.

HANS S. MEYER.

Witnesses:

E. M. WVEBB, W. EDGAR JoNEs. 

